OR/17/006 Geochemistry and land quality

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Monaghan, A A, Dochartaigh, B O, Fordyce, F, Loveless, S, Entwisle, D, Quinn, M, Smith, K, Ellen, R, Arkley, S, Kearsey, T, Campbell, S D G, Fellgett, M, and Mosca, I. 2017. UKGEOS - Glasgow geothermal Energy Research Field Site (GGERFS): initial summary of the geological platform. British Geological Survey Open Report, OR/17/006.

Introduction[edit]

This section summarises current knowledge on the geochemical environment of the land surface (0–0.5 m) in the Clyde Gateway area. It includes information on the geochemistry of stream sediment, stream water and shallow soil, but does not include information on the chemical quality of deeper geological deposits or of groundwater (See Hydrogeology).

The chemical quality of land is an important consideration. Elemental concentrations at any location are controlled by factors such as geology, vegetation, soil forming processes and climate. In addition, environmental concentrations can be enhanced by anthropogenic (man-made) activities such as mining, industrialisation, urbanisation and waste disposal. The distribution of the elements is of concern because 26 are essential to life in small doses but are potentially harmful to plants and animals (including humans) in high doses and a further eight are generally toxic to most organisms. Of further concern are the quantities of persistent organic pollutants (POPs) mainly of man-made origin; many of which are detrimental to health. These include the polynuclear aromatic hydrocarbons (PAHs) and the polychlorinated biphenyls (PCBs) (Fordyce et al., 2012[1]). Some natural rock types such as oil-shales, black algal limestones and black carbonaceous shales and coals are rich in PAHs; hence, their concentrations in underground water resources may be enhanced via contact with these rock types. There is the potential also to intersect liquid and gaseous hydrocarbons, whilst drilling in underground workings that have mined these types of deposit in the past (Appleton et al., 1995[2]).

Substances of concern include also, naturally occurring radioactive materials (NORMS) such as uranium (U), thorium (Th) and potassium (K) and their radioactive decay products such as radium (Ra) and radon (Rn). Radium is relatively short lived, but radon is a natural colourless, odourless gas that is a daughter product of the radioactive decay of uranium in rocks, waters and soils. It can migrate up through rock, water and soil to the surface environment. Radon is a soil gas, but as it reaches the surface it has the potential to impact upon air quality also. Once in open air, radon is normally dispersed, but problems can arise if it enters confined spaces in poorly ventilated buildings where it can accumulate. As a radioactive substance, radon gas exposure has been implicated in lung cancer. The recommended action level in the UK for radon in homes is 200 Becquerels per cubic metre (200 Bq m-3) (PHE, 2016[3]).

Consideration has to be given also to other potentially harmful gases that occur in rocks, waters and soils such as methane (CH4), carbon dioxide (CO2) and hydrogen sulphide (H2S). Methane is a low toxicity gas but when the concentration in air is between 5–15% by volume, ignition will cause an explosion. It is highly flammable; hence potential hazards include fire and explosion. Methane is most commonly produced by the anaerobic breakdown of organic material in landfill or by geological processes such as the burial, compaction and heating of organic material, which is converted into methane-bearing rocks such as coal and oil-shales. Methane is only freely released from rocks either close to geological disturbances such as faults, or as a result of degassing as the coal/shale is fractured during mining. At high concentrations, carbon dioxide is toxic and asphyxiating. It can be produced by oxidation of coal/shale deposits and via biological processes. Carbon dioxide is produced also during oxidation of organic materials in landfill. Hydrogen sulphide is a toxic gas produced by the bacterial reduction of sulphate. Iron sulphide (FeS2) is commonly associated with organic materials in UK coal-bearing and black shale rock types; hence, waters passing through these rocks are often rich in sulphate. Biological breakdown of this sulphate leads to the production of hydrogen sulphide gas. Hydrogen sulphide is produced also by the decomposition of organic matter in land-fill sites and in sewage works. All these gases are known to accumulate in former mine workings in the UK (Appleton et al., 1995[2]). Methane, carbon dioxide and hydrogen sulphide released into open air are quickly diluted, but like radon, problems can arise if they enter poorly ventilated buildings or tunnels. Gas may migrate to the surface via natural faults and cracks as well as via man-made structures such as old coal workings, mine shafts, vents and boreholes. It can enter buildings via cracks in the floor, service ducts, sewerage systems, floor structures, claddings or ventilation ducts (Appleton et al., 1995[2]).

The weathering/oxidation and biological breakdown of pyrite in coal and shale deposits also generates sulphuric acid (H2SO4) leading to acid mine-waters, which can have pH <3. Many metal ions are more soluble in acid waters; hence acid mine drainage often contains elevated concentrations of metals such as iron, nickel, copper, lead, aluminium and manganese. When these waters reach the surface and (i) come into contact with oxygen in the air and (ii) dilution with surface waters raises the pH above 3; the iron precipitates out of the water as iron hydroxides, which form yellow-orange precipitates on stream beds. These can smother aquatic life and can contain elevated concentrations of other potentially harmful metals that precipitate out into the iron hydroxide phases (INAP, 2009[4]).

The toxicity and mobility of all these potentially harmful substances (PHSs) are often controlled by the amount of other elements present, so it is important to understand as fully as possible the chemical composition of the environment. This is necessary to protect the quality of ecosystems and water bodies as well as plant, animal and human health under current UK environmental legislation (HMSO, 1990[5]).

Under this legislation, before any development can take place, site assessments and ground investigations must be carried out to demonstrate that land quality is safe and fit for purpose for the intended use. In addition, the development of subsurface resources such as geothermal energy that have the potential to alter ground conditions should be monitored throughout their life cycle.

This section considers the current understanding of land quality in the Clyde Gateway area and the potential surface environmental impacts of GGERFS geothermal research.

Study area[edit]

Several factors contribute to the chemical quality of surface land and water resources in the Clyde Gateway area (Figure 51). These include natural factors (e.g. underlying bedrock and superficial deposit geology, vegetation, topography and climate) and anthropogenic factors (e.g. current and historic land use, particularly industry, waste disposal, power generation, atmospheric emissions and construction). A brief summary of these factors in the Clyde Gateway area is as follows.

Surface water bodies[edit]

The Clyde Gateway is bisected by the River Clyde, which flows east to west through the area into the Clyde Estuary. The Clyde Gateway area is upstream of the weir that limits the tidal extent of the river. Several smaller streams that flow into the River Clyde are located within the Clyde Gateway area also. These include the Battle, Camlachie, Eastfield, Malls Mire, Polmadie and Tollcross burns (Figure 51). However, for much of their length, these smaller streams are culverted and have only limited surface expression in the Clyde Gateway area (Fordyce et al., 2004[6]).

Bedrock and quaternary geology[edit]

The Clyde Gateway area is underlain by a sequence of Carboniferous sedimentary rocks of the Scottish Coal Measures Group comprising repeated sequences of sandstone, siltstone, mudstone, seat-earth, shale, coal and ironstone. In the River Clyde corridor, these are overlain by Quaternary alluvial superficial deposits (Browne et al., 1999[7]). Concentrations of PHS such as arsenic (As), antimony (Sb), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), fluorine (F), iron (Fe), lead (Pb), mercury (Hg), nickel (Ni), uranium (U), and selenium (Se) can be enhanced in shale, coal and ironstones relative to other rock types; hence where these crop out at surface, the soils and sediments derived from them and water that passes through them can contain elevated concentrations of these chemical elements. However, it is difficult to discern relationships between the underlying geology and soil/sediment/surface water quality in the Clyde Gateway area as the surface environment has been highly altered by human activities (Fordyce et al., 2012[1]).

Current and historic land use[edit]

The Clyde Gateway area has a long history of development dating from the 18th century, with major expansion occurring during the 19th century (Glasgow City Archives, 2016[8]). The area was home to several major industries including coal mining; brick, sand and gravel pits; print and paper works; textile and dye works; potteries; gas works and the former Dalmarnock coal-fired power station (Figure 52). The area was a centre for iron working in the past with major foundries on the western periphery of the area, in Parkhead in the north and on the south side of the River Clyde. The Clydebridge steel works continues to operate at the present day (Figure 52). JJ White’s, the world’s largest chromite ore processing plant during the 19th century, was located in the Shawfield area of the Clyde Gateway. The chromite ore was imported for processing and the plant operated until 1968. Chromite ore processing residues (COPR) were extensively used as landfill material around south-east Glasgow and it is estimated that 2 500 000 tons (dry weight) were deposited during the lifetime of the factory (Farmer et al., 1999[9]). This has had an impact on the nature of artificial ground in the Clyde Gateway area (See Artificial deposits). The former site of the chromite ore processing works at Shawfield has been the subject of a major remediation project over the last 10 years and this is described in more detail in Soil quality.

The Clyde Gateway area was also home to extensive areas of 18th and 19th century sandstone-brick tenement housing, which was of poor quality. Since the Second World War, practically all of this housing has been demolished and replaced with a mixture of 1950–90s terrace, tenement and tower-block social housing. In the last 15 years, the Clyde Gateway area has been designated as a major area of urban regeneration. Under this programme, more of the Victorian-age tenements and some of the latter-20th century housing as well as former industrial sites have been demolished to make way for new housing and commercial developments. The centrepiece for this redevelopment was the site of the 2014 Commonwealth Games, located in Dalmarnock. The Games were used as a vehicle to remediate former industrial land including the site of the old Dalmarnock power station and develop that into athlete’s accommodation (converted to social housing after the Games), a multi-purpose arena, hotels and commercial developments.

As a result of these changes, today the Clyde Gateway area comprises a mix of residential housing, parks, sports facilities, light industry, heavy industry (the Clydebridge Steel works) and commercial developments (Glasgow City Archive, 2016[8]).

Artificial deposits[edit]

Given this complex history and multiple phases of redevelopment, the Clyde Gateway area is extensively underlain by artificial deposits. These comprise made and infilled ground composed of materials that may be natural or artificial in origin from both local and extraneous sources. Typically, artificial ground of this nature is only a few meters thick, but in areas close to former excavations, thicker deposits up to tens of meters may be expected (Browne et al., 1999[7]). Materials such as building rubble, industrial waste, quarry waste and furnace slag are typically used as fill materials (McMillan and Powell, 1999[10]) and depending on their composition can have an impact on soil and stream water and sediment chemistry. An example of this is the presence of chromite ore processing residue (COPR) in the Clyde Gateway area.

Many correspond to former brick and clay pits that were infilled in close proximity to the former JJ White’s chromite works in the south of the Clyde Gateway area. As part of an extensive programme of remediation over the last 20 or so years, investigations into the nature of the COPR have been carried out and these are described in more detail in Soil quality.

Figure 51    Location of BGS geochemistry samples in the Clyde Gateway area. Includes mapping data licensed from Ordnance Survey. © Crown Copyright and/or database right 2017. Licence number 100021290 EUL.
Figure 52    Location of selected current and historic land uses in the Clyde Gateway area. Includes mapping data licensed from Ordnance Survey. © Crown Copyright and/or database right 2017. Licence number 100021290 EUL.

Sources of information on land quality in the Clyde Gateway area[edit]

There are four main sources of information on the geochemistry of the surface environment in the Clyde Gateway area. These are:

  1. British Geological Survey (BGS) — Public Health England (PHE) radon potential assessments
  2. Site investigation reports held by Glasgow City Council (GCC) and South Lanarkshire Council (SLC)
  3. Scottish Environment Protection Agency (SEPA) surface water quality monitoring data
  4. Geochemical surveys carried out by the British Geological Survey (BGS) over the last 15 or so years

Natural gases in soil and BGS-PHE radon potential data[edit]

The potential hazards from methane, carbon dioxide and hydrogen sulphide soil gas across the UK, including the Clyde Gateway area, were documented in a review of natural contamination carried out by the BGS for the Department of the Environment in the 1990s (Appleton et al., 1995[2]). This review reports that historically, the South Lanarkshire coalfield was noted for a number of surface gas emissions, but these appear to have abated as a result of ventilation and dewatering during the development of deep mines after the 1850s (Robinson and Grayson, 1990[11]). Carbon dioxide and hydrogen sulphide gases have been reported at an operational geothermal energy scheme accessing Scottish Coal Measure mine-waters at Cowdenbeath in Fife (Banks et al., 2009[12]) and CO2 emmissions from former coal-mine workings entering homes in two recent housing developments have been reported in Mid Lothian (Othieno, 2016[13]). Other than the information contained within the Appleton et al. (1995)[2] review, no systematic soil gas measurements have been identified within the Clyde Gateway area. Data may exist in site investigation reports held by GCC and SLC and it is recommended that these are assessed as part of a baseline monitoring strategy for the area.

For over 25 years, the BGS and PHE have collaborated to produce maps and datasets documenting potential threats of radon soil gas emissions in the UK. These are based on classifying the country according to the radon generating potential of different rock types depending on their likely uranium composition. This information is combined with data on radon levels in homes held by PHE to produce radon potential rankings for geological polygon areas across the country (PHE, 2016[3]). Recently, the radon potential maps of Scotland have been revised to include the current 1:50 000-scale geological linework (PHE-BGS, 2011[14]). This highlighted a number of new areas designated as of high radon potential, particularly in the Central Belt of Scotland. In the last couple of years, PHE has been testing homes and schools in these areas to validate this prediction. The results of this most recent survey of radon in Scottish homes are due to be published within the next few months. Whether any homes have been surveyed within the Clyde Gateway area is unknown until the data are released, but the new report should provide estimates for likely radon concentration in the area once available.

Site investigation data[edit]

Information on the chemical quality of soil, sediment and surface water either from samples collected at surface or in boreholes is held in numerous site investigation reports held by GCC and SLC. Some of this information is held by BGS also, under varying levels of confidentiality. The benefit of this information is that samples are often collected at a closely spaced sampling density across any given development site. This provides detailed information on the variability of the chemical quality of land on a very local scale. This is important in urban environments where surface deposits are often highly heterogeneous.

The constraints on using this information are as follows:

  1. As a research facility, the aim is for all UKGEOS data and information to be made publically available. Commercial site investigation chemistry information is held under a variety of confidentiality conditions. It’s important to note that land remediation and development will alter site chemistry and the validity of any site investigation data will change through time.
  2. The information from site investigation reports is limited in its spatial extent by the distribution of sites where redevelopment has taken place. These tend to be along transport corridors and in designated regeneration sites rather than providing information for the whole area.
  3. Chemical information held in site investigation records is often held in scanned pdf format and would require digitisation for use in scientific study. Digital records exist already for the Clyde Gateway area; even so, these would require organisation and checking prior to use. These tasks were beyond the scope of this initial assessment.
  4. Chemical data from different site investigations may not be directly comparable. The experience that BGS has had using groundwater chemistry data from site investigation reports in the Clyde Gateway area for the Groundwater and Soil Pollutants (GRASP) project (Fordyce et al., 2014[15]) is that samples from adjacent sites may have been collected and analysed in different ways in different laboratories. This makes comparison between adjacent sites difficult. Even when samples have been analysed by the same method in the same laboratory, but at different times, changes in calibration of the machines between analytical batches means that results may not be directly comparable. For example, concentrations of arsenic in soil from site A may be reported in the range 5–35 mg/kg whereas soil arsenic concentrations in an immediately adjacent site B may be reported as 10–80 mg/kg. The assumption would be that soils in site B contain more arsenic than site A. However, the apparent difference in results may be purely an artefact of different sampling and analytical methods and the arsenic content of both sites may be rather similar.

SEPA surface water quality monitoring data[edit]

The SEPA has water quality monitoring stations on the River Clyde at Dalmarnock Bridge and Rutherglen Bridge within the Clyde Gateway area. They have two further stations, one at Cambuslang Road Bridge and one at the Clyde Tidal Weir immediately upstream and downstream of the Clyde Gateway area respectively. Time-series water quality monitoring data will be available from these stations, including parameters of interest to the baseline monitoring of environmental conditions for geothermal energy, including water temperature, pH, dissolved oxygen, total organic matter content (TOC) and a range of inorganic chemical parameters. It was beyond the scope of this initial assessment to request and review these data, but it is recommended that this should form part of further assessments of the Clyde Gateway area as these data should be publically available from the SEPA.

For reasons of time and ready availability of data, this report focusses on the systematic geochemical information that has been collected by the BGS across the Clyde Gateway area over the last 15 years.

BGS geochemical information[edit]

The BGS has carried out a number of systematic geochemical surveys of the surface environment in the Glasgow area over the last 15 years. These include three main sources of information on land quality in the area:

  1. The Estuarine Contamination Project survey of sediment and water quality in the River Clyde Estuary
  2. The G-BASE-GCC survey of stream sediment and stream water quality in all tributaries of the River Clyde within the GCC area — The Clyde Tributaries project
  3. The Geochemical Baseline Survey of the Environment (G-BASE) soil survey of Glasgow

These projects provide information on the chemical quality of soils, stream sediments and waters within the Clyde Gateway area. Systematic projects such as G-BASE avoid the issues of differences between analytical runs outlined in Site investigation data, by careful quality control procedures, including the insertion of cross reference standards between analytical batches. Therefore, it is possible to assess the quality of the surface environment across the area using these datasets. For this report, and to place the Clyde Gateway area in the context of the immediate surroundings, a buffer zone of 0.5 km beyond the that of Clyde Gateway is used to assess the geochemical information from the three projects (Figure 51).

Clyde estuary sediment and water data[edit]

Water and grab sediment samples were collected at the same locations from the River Clyde as part of the BGS Estuarine Contamination project in 2003. Full details of the sampling and analytical methods are provided in Jones et al. (2004)[16]. The samples were analysed for a suite of approximately 50 inorganic and organic chemical parameters (Table 1). The Clyde Gateway and its buffer zone contain five water samples collected from the River Clyde, but only one of these is located within Clyde Gateway itself, at the junction of the Polmadie Burn with the River Clyde (Figure 51). None of the River Clyde sediment samples collected as part of this project lie within either the Clyde Gateway or Clyde Gateway buffer zone.

G-BASE-GCC Clyde tributaries stream sediment and water data[edit]

Water and grab sediment samples were collected from the same locations from every kilometre of length of the tributaries draining into the River Clyde within the GCC area under a joint G-BASE-GCC Clyde Tributaries project in 2003. Full details of the sampling and analytical methods are provided in Fordyce et al. (2004)[6]. The samples were analysed for a suite of approximately 50 inorganic and organic chemical parameters (Table 17). Sixteen of the stream water samples are located within the Clyde Gateway and its buffer zone and of these, five are within the Clyde Gateway itself. These were collected from the Camlachie, Eastfield, Malls Mire, Polmadie and Tollcross burns (Figure 51). Where possible samples were collected from open sections of the streams, but in the cases of the Camlachie and Malls Mire burns, GCC provided assistance and manhole access for the collection of samples from culverted sections of the streams. In some cases there was no sediment present in the culverts at the time of sampling. Therefore, there are fewer sediment than water samples in the area; 13 in the Clyde Gateway buffer zone and four in the Clyde Gateway area (Figure 51).

G-Base soil data[edit]

Top (5–20 cm) and deeper (35–50 cm) soil samples were collected from the same locations on a systematic 500 m grid sampling scheme across the Glasgow area by the G-BASE project in 2001–2002. This was part of a programme to characterise the chemical quality of urban soils across Glasgow. Full details of the sampling and analytical methods are provided in Fordyce et al. (2012)[1]. The samples were analysed for a suite of approximately 50 inorganic chemical parameters (Table 17). The G-BASE project carried out a further phase of work to characterise soil quality across the wider Clyde Basin in 2010–2011. As part of this programme, additional sampling was carried out in the Glasgow city area to determine organic contaminant (POP) concentrations in urban topsoils (5–20 cm). These Organic Pollutants in Urban Soil (OPUS) samples were collected from selected land use types and underwent total petroleum hydrocarbon (TPH), PAH and PCB analysis in addition to a full suite of inorganic parameter determinations (Table 17). Full details of the sampling and analytical methods are provided Kim et al. (In prep)[17]. As a result of these surveys, there are 100 G-BASE soil samples within the Clyde Gateway buffer zone and 41 within the Clyde Gateway area (Figure 51). Of these, seven OPUS samples with POP determinations are located in the Clyde Gateway area.

The numbers of BGS stream sediment, stream water and soil samples within the Clyde Gateway area are summarised in Table 18.

Table 17    Parameters determined in BGS stream sediment,
stream water and soil samples in the Clyde Gateway area.
Inorganic Parameters Name Units in Water Units in Sediment Units in Soil
Ag Silver NA mg/kg mg/kg
Al Aluminium µg/L wt% wt%
As Arsenic µg/L mg/kg mg/kg
Ba Barium µg/L mg/kg mg/kg
Be Beryllium µg/L NA NA
Bi Bismuth µg/L mg/kg mg/kg
Br Bromine NA mg/kg mg/kg
Ca Calcium mg/L wt% wt%
Cd Cadmium µg/L mg/kg mg/kg
Ce Cerium µg/L mg/kg mg/kg
Cl Chlorine mg/L NA NA
CN Cyanide NA mg/kg mg/kg
Co Cobalt µg/L mg/kg mg/kg
Cr Chromium µg/L mg/kg mg/kg
Cs Caesium µg/L mg/kg mg/kg
Cu Copper µg/L mg/kg mg/kg
DO Dissolved Oxygen mg/L NA NA
EC Electrical Conductivity µS/cm NA NA
F Fluorine mg/L NA NA
Fe Iron mg/L wt% wt%
Ga Gallium NA mg/kg mg/kg
Ge Germanium NA mg/kg mg/kg
HCO3 Alkalinity mg/L NA NA
Ho Holmium µg/L NA NA
Hf Hafnium NA mg/kg mg/kg
Hg Mercury µg/L mg/kg mg/kg
I Iodine NA mg/kg mg/kg
In Indium NA NA mg/kg
K Potassium mg/L wt% wt%
La Lanthanum µg/L mg/kg mg/kg
Li Lithium µg/L NA NA
Mg Magnesium mg/L wt% wt%
Mn Manganese mg/L wt% wt%
Mo Molybdenum µg/L mg/kg mg/kg
Na Sodium mg/L wt% wt%
Nb Niobium NA mg/kg mg/kg
Nd Neodymium NA NA mg/kg
Ni Nickel µg/L mg/kg mg/kg
NH4 Ammonium mg/L NA NA
NO3 Nitrate mg/L NA NA
P Phosphorus mg/L wt% wt%
Pb Lead µg/L mg/kg mg/kg
pH pH pH units pH units pH units
Rb Rubidium µg/L mg/kg mg/kg
Sb Antimony µg/L mg/kg mg/kg
Sc Scandium NA mg/kg mg/kg
Se Selenium µg/L mg/kg mg/kg
Si Silicon mg/L wt% wt%
Sm Samarium NA NA mg/kg
Sn Tin µg/L mg/kg mg/kg
SO4 Sulphate mg/L NA NA
S Sulphur mg/L NA mg/kg
Sr Strontium mg/L mg/kg mg/kg
Ta Tantalum NA mg/kg mg/kg
Te Tellurium NA mg/kg mg/kg
TDS Total Dissolved Solids mg/L NA NA
Th Thorium µg/L mg/kg mg/kg
Ti Titanium NA mg/kg mg/kg
Tl Thallium µg/L mg/kg mg/kg
U Uranium µg/L mg/kg mg/kg
V Vanadium µg/L mg/kg mg/kg
W Tungsten NA mg/kg mg/kg
Y Yttrium µg/L mg/kg mg/kg
Yb Ytterbium NA NA mg/kg
Zn Zinc µg/L mg/kg mg/kg
Zr Zirconium µg/L mg/kg mg/kg
Organic Parameters
LOI Loss on Ignition NA NA wt%
PAH Polycyclic Aromatic Hydrocarbons NA mg/kg mg/kg
PCB Polychlorinated Biphenyls NA µg/kg µg/kg
TIC Total Inorganic Carbon mg/L NA NA
TOC Total Organic Carbon mg/L wt% NA
TBT Tributyltin Tin NA mg/kg NA
TPH Total Petroleum Hydrocarbons NA mg/kg mg/kg
NA = not analysed
Table 18    Number of BGS stream sediment, stream water
and soil samples in the Clyde Gateway area.
Sample Type Clyde Gateway Buffer Zone Clyde Gateway
Estuary River Clyde Sediment 0 0
Estuary River Clyde Water 5 1
Clyde Tributaries Stream Sediment 13 4
Clyde Tributaries Stream Water 16 5
G-BASE Topsoil (5–20 cm) 100 41
G-BASE Deeper Soil (35–50 cm) 90 33
G-BASE OPUS Topsoil (5–20 cm) 8 7

Geochemical quality of the Clyde Gateway area surface environment[edit]

On the basis of the BGS geochemistry datasets, the chemical quality of stream sediment, stream water and soil is summarised as follows. In the absence of major changes in land use, the distribution of the majority of these chemical substances in soils and stream sediments are fairly stable through time; hence although the BGS surveys were carried out over 10 years ago; the results are likely to be representative of conditions on the ground today. Stream water chemistry is more variable through time and the data presented here are a spatial snapshot (See Stream water quality). Maps of parameter concentrations in BGS stream sediment, stream water and soil across the Clyde Gateway area are presented in Appendix 1 - BGS geochemical maps of the Clyde Gateway area surface environment.

When considering land quality it is useful to make comparisons to environmental guideline values that exist to protect ecosystems, aquatic bodies and plant animal and human health from exposure to PHS in the surface environment. The guidelines used for comparison in this assessment are outlined in Table 19. The soil quality guidelines are designed to protect against human exposure to soil and are land use specific. Called either generic assessment soil guideline values (SGV) or soil screening levels (SSL) these criteria represent the values below which land is not considered to be contaminated. Exceedance of the guideline does not mean that land is contaminated, rather that further investigations need to be carried out (EA, 2009[18]; DEFRA, 2014[19]).

Soil quality[edit]

The concentrations of inorganic chemical parameters in topsoil (5–20 cm) across the Clyde Gateway area are presented as interpolated surface maps showing the data distribution, as there is systematic data coverage across the whole area. These were generated in an ArcMap® geographic information system (GIS) using the inverse distance weighting interpolation function, based on a grid size of 80 m and search radius of 500 m. Whilst the G-BASE soil sample density of 1 per 0.25 km2 is relatively detailed for a city-wide survey; it is still not closely spaced enough to capture the variability in concentration for all the parameters due to the highly heterogeneous nature of urban soils. As such, there is a degree of uncertainty in extrapolating the data between known points and caution should be exercised when viewing the maps. Nonetheless, the maps provide an overview of soil geochemistry across the Clyde Gateway area. Only seven OPUS soil samples underwent POPs analysis in the area; hence, organic pollutant information is presented in the form of symbol maps.

Inorganic parameters were measured in deeper soil samples (35–50 cm) also. Whilst not the subject of this review due to time constraints, these show similar distributions to those in topsoil, but parameter concentrations vary between top and deeper soils across the area. In some cases, parameter concentrations can be higher in deeper soil due to the presence of artificial ground and waste materials. A fuller explanation of these relationships is given in Fordyce et al. (2012)[1]. This review focuses on topsoil (5–20 cm) chemistry as follows.

Inorganic substances[edit]

Comparison of the 41 G-BASE topsoil samples from the Clyde Gateway area to the UK soil quality guidelines reveals that of the parameters listed in Table 19, concentrations in excess of the suggested allotment SSLs (91 mg/kg V; 620 mg/kg Zn) are reported in two allotment topsoils for vanadium and one for zinc (Fordyce et al., 2012[1]). However, these are not UK legislative guidelines; rather they are proposed standards by the environmental consultancy industry and there is a deal of uncertainty in the derivation of these values (Nathanail et al., 2015[20]). As such, exceedance of these SSLs does not equate to risk; rather that further studies may be advisable. Four soils contain cadmium concentrations above the UK allotment SSL of 1.8 mg/kg (DEFRA, 2014[19]), but none are allotment soils; hence the guideline is not exceeded.

Higher soil-As concentrations in the Clyde Gateway area are associated with the present day industrial estate at Shawfield, which was the site of the former chromite ore processing works; and with the steel mill at Clydebridge (Figure 70 in Appendix 1). Arsenic and copper concentrations above the residential SSLs of 37 mg/kg (DEFRA, 2014[19]) and 520 mg/kg (Nathanail et al., 2015[20]) respectively are recorded at one site in Shawfield, but this is not a residential soil; hence the guidelines are not exceeded.

These areas also correspond to higher topsoil chromium (Figure 71 in Appendix 1), nickel (Figure 72 in Appendix 1) and lead (Figure 73 in Appendix 1) concentrations as a consequence of their metal processing history. Similarly, soil calcium contents are higher at these locations as lime was used in both chromite ore processing and steel production. The combination of high calcium-chromium-nickel is indicative of the presence of waste from these industries in the soils, which tends to be alkaline in nature (Figure 74 in Appendix 1). In other parts of the Clyde Gateway area, higher soil-lead concentrations are reported from a former gas works site and from artificial ground over a former reservoir (Figure 73 in Appendix 1); and higher soil chromium and nickel are associated with a former colliery, again reflecting historic land use (Figures 71 and 72 in Appendix 1).

Concentrations of nickel above the UK SGV of 130 mg/kg for residential land use (EA, 2009[18]) are reported at six sites; however, none are residential soils; hence the guideline is not exceeded. For lead, two allotment soils exceed the SSL of 80 mg/kg and two residential soils exceed the SSL of 200 mg/kg (DEFRA, 2014[19]). However, this does not mean that land is contaminated, rather that further investigations may be required.

Very high concentrations of soil-Cr (up to 4286 mg/kg) are reported in the Shawfield area associated with the COPR waste (Figure 71 in Appendix 1). Despite the presence of COPR in the area, only one allotment soil exceeds the former UK SGV of 130 mg/kg for this land use type. Similarly, only one domestic garden soil exceeds the former UK SGV for Cr in residential soils of 200 mg/kg (EA, 2002[21]). In terms of toxicity, the speciation of chromium is important. Under natural conditions, chromium is normally present as the CrIII form and is an essential trace element for health. However, the CrVI hexavalent form is a known carcinogen to humans via inhalation. CrVI is rare in natural environments, but is generated by industrial processes. Therefore, the old SGVs have been superseded by SSL that take into account the speciation of Cr and the concentration of CrVI in particular (DEFRA, 2014[19]). The G-BASE dataset does not contain information on the CrVI content of soil, but the former chromite ore works site at Shawfield has been the subject of much study and a major regeneration programme over the last 15 or so years. Work by Bewley et al. (2001)[22] and Hillier et al. (2003)[23] revealed that the COPR material was over 10 m thick in places and was highly alkaline and soluble and contained very high concentrations of both CrIII (up to 49 500 mg/kg) and CrVI (up to 15 600 mg/kg).

Broadway et al. (2010)[24] investigated CrVI concentrations in 21 of the highest total-Cr concentration G-BASE Glasgow urban topsoils and a further six samples collected from known COPR waste sites. Results revealed that CrVI concentrations ranged between <1.89–1485 mg/kg. However, concentrations in excess of the new most precautionary (residential land use) DEFRA (2014)[19] SSL of 21 mg/kg CrVI were present in three of the topsoils from the known Cr-waste sites only. None of these soils were from residential land uses. Two of the samples were located at Shawfield in the Clyde Gateway area. Further tests to examine possible human bioaccessibility via the ingestion exposure route showed that CrVI in the soil was reduced to CrIII in the gut and was of less concern for human uptake. However, simulations of inhalation exposure on two of the Cr-waste soils, suggested that CrVI may be bioavailable. Hence, inhalation of polluted dusts may be a potential consideration in the area (Broadway et al., 2010[24]).

The Cr-waste sites in Glasgow have undergone significant remediation in recent years including lining and diverting of water courses away from the waste dumps, in situ chemical treatments with calcium polysulphide and capping/containment of the waste materials to mitigate the impacts on soil and water quality and human interaction (Bewley and Sojka, 2013[25]). This work has taken place since the G-BASE survey was carried out in 2001–2002; hence soil-Cr concentrations may now be lower in the area.

Persistent Organic Pollutants (POPS)[edit]

Comparison of the seven G-BASE OPUS topsoil samples from the Clyde Gateway area to the UK soil quality guidelines reveals that of the parameters listed in Table 19, none of the soils exceed current UK POPs guidelines for the particular land use.

The distribution of total petroleum hydrocarbons (TPH) across the area is shown in Figure 75 in Appendix 1. However, no soils are above the suggested most precautionary SSL for TPH of 1200 mg/kg (residential land use) (Nathanail, et al., 2015[20]). Highest concentrations are associated with soil from a road verge adjacent to a petrol station at a busy road junction; soil from a former gas works site and soil from an allotment on artificial ground over a former reservoir. This map gives some indication of TPH concentrations in the surface environment. This is an important baseline dataset since geothermal boreholes are likely to access waters in contact with coal and shales, which may contain naturally higher TPH contents than other rock types.

Concentrations of the PAH benzo(a)pyrene are above the UK residential SSL of 3 mg/kg (DEFRA, 2014[19]), in two soils, but neither were collected from residential land use, so the guideline is not exceeded. One is from a former gas works site and the other from an allotment on artificial ground over a former reservoir (Kim et al., In Prep[17]) (Figure 76 in Appendix 1). Concentrations of topsoil dibenz(a, h)anthracene are higher than the suggested SSL for residential land use of 0.3 mg/kg (Nathanail et al., 2015[20]) at these sites also and at the site of a petrol station road verge, but again none are residential land uses; hence, the guideline is not exceeded (Figure 77 in Appendix 1).

Stream sediment quality[edit]

There are no freshwater sediment quality regulations for the UK, but comparison of the Clyde Gateway area sediments with the Canadian guidelines reveals that of the parameters listed in Table 19, the probable effect concentration (PEC) to protect aquatic life is exceeded by chromium in the Camlachie, Polmadie, Malls Mire and Eastfield Burns. All these streams drain areas of COPR waste disposal; hence the elevated values. Very high concentrations of 2345 mg/kg are reported in the Polmadie Burn which drains the former chromite ore processing works site at Shawfield (Figure 78 in Appendix 1). Whalley et al. (1999)[26] investigated chromium concentrations in sediments from 13 sites from the upper reaches of the River Clyde catchment to the Inner Estuary and found similarly high concentrations in sediments in the Polmadie Burn (3600 mg/kg) and River Clyde (6600 mg/kg) immediately downstream of the Polmadie Burn. High concentrations of chromium in sediment were evident up to 1 km downstream of this input.

However, since these studies have taken place the Shawfield site has been extensively remediated (see Section 6.4.1). Since the remediation, Palumbo-Roe et al. (2013)[27] have carried out determinations of chromium speciation in sediment pore waters in the Polmadie Burn to assess its mobility from the polluted sediments into the water column. Interestingly, CrVI concentrations were low in the sediment pore water, despite very high total chromium concentrations (up to 12 500 mg/kg) in the sediment. This indicates that high-Cr bearing sediment is still present downstream of the Shawfield site in the Polmadie Burn, but that this may not be readily mobilised into the water column. An ongoing joint PhD studentship between Edinburgh University and the BGS is examining these relationships further, exploring chromium speciation in sediment, pore water and stream water in the Polmadie Burn to improve understanding of chromium mobility and pollutant migration in such post- industrial settings (Sim et al., 2015[28]).

Geothermal energy research is unlikely to impact upon sediment quality directly, beyond the concerns of increased sedimentation during any construction process that disturbs the ground. It may have an indirect impact only if (i) there is connectively between the groundwater resources utilised and the surface water system and (ii) hydrogeological and hydrological flow regimes are changed.

Stream water quality[edit]

Neither surface water nor groundwater in Glasgow are used as a drinking water resource. Hence, the main concerns for water quality centre on ecological protection under the Water Framework Directive (WFD) (CEC, 2008[29]). The BGS Clyde Estuary and G-BASE-GCC Clyde Tributary stream water samples were collected across the Glasgow area during 2002 and provide a spatial overview of stream water quality (Fordyce et al., 2004[6]; Jones et al., 2004[16]). However, samples were collected only once and as such are a spatial snapshot. Time-series monitoring would be required to provide baseline water quality information for GGERFS as water quality changes in response to factors such as climate, weather, season, flow and storm events.

As an initial assessment, comparison of the BGS surface water chemistry results to the WFD freshwater Environmental Quality Standards (EQS) indicates that for the substances outlined in Table 19, only ammonium, chromium, phosphorus and dissolved oxygen (DO) exceeded the guidelines as follows.

Ammonium, chromium, phosphorus concentrations are above the recommended EQS and DO below the recommended EQS in the Polmadie Burn (Figures 79–82 in Appendix 1). This stream drains the former chromite ore works site in Shawfield; hence the high concentrations of Cr in the burn water (126 µg/L) and elevated values in the River Clyde water at the tributary junction with the Polmadie Burn (5 µg/L). Indeed, very high concentrations of Cr (9100 µg/L) have been reported in groundwater at the Shawfield site resulting in very elevated values (6700 µg/L) in the Polmadie waters and 1100 µg/L in the River Clyde (Farmer et al., 2002[30]). Similarly, Cr concentrations of 16 9000 µg/L in groundwater and 3100–6200 µg/L in stream waters from the Polmadie Burn were reported from the site by Whalley et al. (1999)[26]. By contrast, Cr concentrations in samples of river water from 13 sites along the River Clyde were below the limit of detection with the exception of waters immediately downstream of the Polmadie Burn inflow, which contained 1100 µg/L. At sampling points 1 and 4 km downstream of the inflow, values of 10 µg/L were recorded indicating rapid dilution of the stream water inputs in the river system. The studies by Farmer et al. (2002)[30] demonstrated that >90% of the Cr present in south-east Glasgow was in the more toxic CrVI hexavalent form and was associated with humic substances in the waters. Similarly, Whalley et al. (1999)[26] showed that the groundwaters from the Shawfield site, stream waters from the Polmadie Burn and River Clyde waters downstream of the Polmadie Burn contained Cr in the more toxic hexavalent form. However, since these studies and the BGS surveys have taken place, the Shawfield site has been extensively remediated (See Soil quality).

Within the Clyde Gateway area, high chromium concentration above the EQS is reported also in the Eastfield Burn water, which drains another area of COPR waste (Figure 80 in Appendix 1). Phosphorus exceeds the EQS also in the Malls Mire, Eastfield and Tollcross Burns probably because these urban streams are culverted for significant parts of their length (Figure 81 in Appendix 1). This restricts sunlight and oxygenation, which in turn limit biological nutrient processing. For similar reasons, DO is lower than the recommended EQS in these streams and the Battle Burn (Figure 82 in Appendix 1).

There are no freshwater EQS for uranium in water in the UK; however, none of the stream water samples in the Clyde Gateway area exceed the Canadian freshwater EQS of 15 µg/L (Figure 83 in Appendix 1). It is important to consider uranium in water, as deep mine-waters in rock sequences containing coal and shale that may contain elevated concentrations of NORMs such as uranium.

Stream water pH in the Clyde Gateway area is circum neutral to alkaline (pH 6.8–8.3) and above the recommended EQS (Figure 84 in Appendix 1). Acid mine drainage (AMD) is often associated with coal mining and is a consideration in geothermal development in general based on mine-waters (Banks et al., 2009[12]). However, if present, this is only likely to impact on surface water quality if there is connectivity between groundwater and surface water resources. It will be important to establish these relationships and baseline conditions prior to any geothermal research.

Table 19    Stream water, stream sediment and soil environmental quality guidelines used in the present assessment.
Substance UK Freshwater EQS Canadian <2 mm Freshwater
Sediment PEC
UK SGV/SSL for Residential
(R)/Allotment (A) Soils
Reference CEC (2008)[29]*
UKTAG (2010)#
EA (2013a)[31]`
CCME (2011)[32]¬
MacDonald et al. (2000)[33] EA (2002)[21]~
EA (2009)[18]+
DEFRA (2014)[19]^
CL:AIRE (2010)[34]
Nathanail et al. (2015)[20]$
Arsenic (As) 50 µg/L# 33 mg/kg 37 mg/kg (R)^
Antimony (Sb) 550 mg/kg (R)”
Barium (Ba) 1300 mg/kg (R)”
Cadmium (Cd) 0.09 µg/L* 4.98 mg/kg 1.8 mg/kg (A)^
Chromium (Cr) 4.7 µg/L# 111 mg/kg 130 mg/kg (A)~
200 mg/kg (R)~
Copper (Cu) 10 µg/L# 149 mg/kg 520 mg/kg (A)$
Iron (Fe) 1 mg/L#
Lead (Pb) 7.2 µg/L* 128 mg/kg 80 mg/kg (A)^
200 mg/kg (R)^
Mercury (Hg) 0.05 µg/L* 1.06 mg/kg 1 mg/kg (R)^
Molybdenum (Mo) 670 mg/kg (R)”
Nickel (Ni) 20 µg/L* 48.6 mg/kg 130 mg/kg (R)+
Nitrate (NO3) 30 mg/L`
Phosphate (P2O5) 0.1 mg/L`
Selenium (Se) 120 mg/kg (A)+
Uranium (U) 15 µg/L¬
Vanadium (V) 91 mg/kg (A)$
410 mg/kg (R)$
Zinc (Zn) 75 µg/L# 459 mg/kg 620 mg/kg (A)$
Ammonium (NH4) 1 mg/L (Fisheries)*
PAH 22.8 mg/kg
PCB 676 µg/kg
TPH 1200 mg/kg (R)$
Benzo(a)pyrene (BaP) 3 mg/kg (R)^
Dibenz(a,h)anthracene (DAB) 0.3 mg/kg (R)$
pH 6.5 (Class 2)*
Dissolved Oxygen (DO) 6 (Class 2)*

EQS = Environmental Quality Standard    SSL = Soil Screening Level    Class 2 = Class 2 rivers    PEC = Probable Effect Concentration SGV = Generic Assessment Criteria Soil Guideline Value

Footnote: The most recent soil protection legislative guidelines are the SSLs for arsenic, cadmium, chromium (Cr) VI, lead, mercury and benzo(a)pyrene (BaP) (DEFRA, 2014[19]). The previous SGVs for nickel and selenium are still in use also (EA, 2009[18]). Reference is made here to the former total chromium SGV because CrVI was not analysed in the G-BASE dataset. Similarly, the G-BASE dataset contains no information on mercury soil concentrations. In addition, to the SSL and SGVs listed above, the environmental consultancy industry has proposed SSLs for antimony, barium, copper, molybdenum, vanadium, zinc and dibenz(a,h)anthracene (DAB) (CL:AIRE, 2010[34]; Nathanail et al., 2015[20]). Whilst these are commonly used in site investigation practice, they are not UK legislative guidelines.

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